Abstract: The chemotaxis behaviors of the nematode Caenorhabditis elegans cultivated at various temperatures (15 degrees C, 20 degrees C and 25 degrees C) were examined at various temperatures (10 degrees C, 15 degrees C, 20 degrees C and 25 degrees C) to determine the multi-sensory integration of physical (thermal) and chemical sensory information within its nervous system. Chemotaxis behavior toward sodium acetate and ammonium chloride were differently affected by both assay and cultivation temperatures, suggesting that the temperature effect on chemotaxis is not general, but rather distinctive for each chemosensory pathway. Since thermosensory cues are likely encountered constantly in C. elegans, we supposed that the chemotaxis behaviors of worms are achieved by the integration of chemo- and thermosensory information. To verify the possible contribution of thermosensory function in chemotaxis, we examined the chemotaxis behaviors of ttx-1(p767) mutant worms with defective AFD thermosensory neurons. The chemotaxis behaviors toward sodium acetate or ammonium chloride of mutant worms cultivated at 20 degrees C and 25 degrees C were reduced relative to those of wild-type worms. These results indicate the important role of multi-sensory integration of chemosensory and thermosensory information in chemotaxis behavior of the C. elegans.

Abstract: A memory of prior thermal experience governs Caenorhabditis elegans thermotactic behavior. On a spatial thermal gradient, C. elegans tracks isotherms near a remembered temperature we call the thermotactic set-point (T(S)). The T(S) corresponds to the previous cultivation temperature and can be reset by sustained exposure to a new temperature. The mechanisms underlying this behavioral plasticity are unknown, partly because sensory and experience-dependent components of thermotactic behavior have been difficult to separate. Using newly developed quantitative behavioral analyses, we demonstrate that the T(S) represents a weighted average of a worm's temperature history. We identify the DGK-3 diacylglycerol kinase as a thermal memory molecule that regulates the rate of T(S) resetting by modulating the temperature range of synaptic output, but not temperature sensitivity, of the AFD thermosensory neurons. These results provide the first mechanistic insight into the basis of experience-dependent plasticity in this complex behavior.

Abstract: The medial prefrontal cortex has been associated with fear, anxiety and stress regulation, and has recently been suggested to play a crucial role in the development of behavioural changes in response to stress. In this study, we evaluated medial prefrontal cortex (mPFC) involvement in both anxiety-like behaviour and increased anxiety-like responses induced by uncontrollable restraint. Rats with mPFC electrolytic lesions (n=7) and sham-lesioned (n=8) were tested in the elevated T-maze (ETM). Restrained rats with mPFC lesions (n=8) and sham-lesioned rats (n=6) were tested in the elevated T-maze 24h after restraint. Both two-trial passive avoidance and one-trial escape behaviours were assessed. The results revealed that mPFC lesions impair passive avoidance, but not escape behaviour. In addition, decreased anxiety-like behaviour in both passive avoidance and escape behaviours were observed in restrained rats with mPFC lesions. Our results suggest that mPFC is important in mediating both anxiety-like behaviour expression and long-term anxiogenic-like effects induced by acute restraint.

Abstract: The exposure to stress at different developmental time points has long been postulated to have a crucial impact on various brain structures involved in mental disorders. The long-term specific effects seem to emerge as a function of timing and duration of the exposure to stress, as well as the characteristics of the stressor. Previous studies have addressed this issue with an effort to describe a single “hyper-sensitive” time point, and have led to disagreement on a particular sensitive period for stress exposure. The primary aim of our study was to investigate the hypothesis that indeed there is a developmental stress risk window in male Wistar rats. We conducted a systematic mapping of the long-term effects of an acute stress protocol, applied both prenatal (gestational days 14-16) and postnatal (days 9-151), overall at 11 different time-points during development. Stress protocol consists of 3 days of either maternal separation (for rats at postnatal days 9-19) or exposure to the stressors forced swim, elevated plus maze and restraint (for both dams and males at postnatal days 24-151). Consequences in adulthood were measured by investigating the animals' behavior in both the open field and startle box, together with the physiological measure of corticosterone. We found both behaviorally and physiologically that the pubescence time points are the most vulnerable to stress compared to all other tested time points along the developmental trajectory. Carefully considering the comparison between rat and human age, our findings may imply the importance of childhood-to-adulthood transition, as a sensitive time-point which may exacerbate a predisposition for the development of stress-induced psychopathologies.

Abstract: The Morris water maze (MWM) was described 20 years ago as a device to investigate spatial learning and memory in laboratory rats. In the meanwhile, it has become one of the most frequently used laboratory tools in behavioral neuroscience. Many methodological variations of the MWM task have been and are being used by research groups in many different applications. However, researchers have become increasingly aware that MWM performance is influenced by factors such as apparatus or training procedure as well as by the characteristics of the experimental animals (sex, species/strain, age, nutritional state, exposure to stress or infection). Lesions in distinct brain regions like hippocampus, striatum, basal forebrain, cerebellum and cerebral cortex were shown to impair MWM performance, but disconnecting rather than destroying brain regions relevant for spatial learning may impair MWM performance as well. Spatial learning in general and MWM performance in particular appear to depend upon the coordinated action of different brain regions and neurotransmitter systems constituting a functionally integrated neural network. Finally, the MWM task has often been used in the validation of rodent models for neurocognitive disorders and the evaluation of possible neurocognitive treatments. Through its many applications, MWM testing gained a position at the very core of contemporary neuroscience research.